Modern manual transmissions are generally constructed in such a way that a plurality of gear wheels, which are fixedly arranged on a drive shaft, continuously engage with freely rotatable gear wheels that are respectively assigned to them and are arranged on a second drive shaft. In order to engage a gear, one of the idlers is rotationally coupled with the assigned drive shaft so that the drive torque of the first drive shaft is transferred to the second drive shaft and from there, ultimately, to a transmission output shaft.
In order to have shock-free, noiseless and low-wear shifting when engaging a gear, it must be ensured that the idler to be coupled and the assigned transmission shaft have at least approximately the same speed. For this kind of speed synchronization, small dimension friction couplings can be used inside the transmission which, before engaging, frictionally mesh by positive locking coupling devices, thus adjusting the two different speeds to each other.
In another synchronization process, the input side drive shaft, which carries either the fixed wheels or the idlers, is brought to a speed, either through acceleration, by way of the drive engine, or by braking, using a gear brake, such that the speeds of the idler to be coupled and assigned gear shaft are essentially equal so that in this way synchronization is possible without friction couplings.
By definition, in the present invention, the gear shafts that can be connected to the drive engine of a motor vehicle via the input clutch, or the drive clutch, are subsumed under the terms “input side gear shaft assembly,” while the shafts that are permanently connected to the drive gears are designated as “output side shafts”.
As is generally known, in order to shift into a lower gear, the input side gear shaft assembly must be brought to a higher rotational speed. This is achieved in that after disengaging the previous gear, the starting clutch is engaged and the engine speed is increased, via an engine control unit, until the speed required for engaging the positive-locking clutch is reached. In order to up-shift, the speed of the input side gear shaft assembly must be reduced. This is achieved in that after disengaging the previous gear, the input side gear shaft arrangement is braked using a gear brake that interacts with one of the gear shafts, until the speed required for engaging the clutch is reached.
Synchronization, by way of the drive engine or a gear brake, is applicable in a simple way particularly to automatic transmissions, which already have an engine control and a transmission control. However, the functional principle can also be applied to manual-shift transmissions.
Conventional manual transmissions comprise an input shaft that is connected to the drive engine, via a drive clutch; a countershaft that is connected to it, via a fixed gear wheel connection, which carries a plurality of fixed gears; a drive-coupled output shaft that is permanently connected with the drive wheels of the vehicle. The idlers assigned to the fixed gear wheels being arranged on the output shaft and are individually connectable in a rotationally fixed manner with the output shaft in the way described above. In addition, manual transmissions with two countershafts are also known, which allow a particularly short manual transmission design. According to the definition shown above, the input shaft and the countershaft or the countershafts, form the input side gear shaft arrangement, with which the gear brake interacts. The present invention is exemplified on the basis of this type of manual transmission where, however, it should be pointed out, that the invention is applicable analogously to other transmission designs.
DE 10 2004 045 828 A1 already describes a manual transmission in which the gear brake is configured as an internal brake, which is arranged inside the transmission housing and interacts with a countershaft. The same document also mentions that the gear brake is “arranged immediately adjacent to the transmission”, and that it can be executed as an external brake. It has also been proposed that an external gear brake be allowed to interact with a PTO shaft (PTO=Power Take-Off) originating at the transmission housing and being drive-connected with a countershaft. The power take-off shaft is provided for driving an auxiliary device or an attached device, for example the hydraulic pump for supplying hydraulic implements. In that type of arrangement, however, the PTO output is no longer available for the actual PTO function.
Against this background, the task of the present invention is to provide a gear braking device with which, despite a gear brake being assigned to a power take-off shaft, a PTO function of the power take-off shaft is possible for driving devices external to the transmission.